1. Field of the Invention
This invention concerns a quantum cascade laser that makes use of intersubband transitions in a quantum well structure.
2. Related Background Art
Light of the middle infrared wavelength range (for example, wavelengths of 3 to 10 μm) is deemed important in various fields, such as medical fields, biomedical measurement, environmental measurement, etc. There are thus increasing needs for a high-performance coherent light source for this wavelength range.
However, a laser light source using normal interband transitions operates only at low temperature in the middle infrared range, and a laser light source capable of operation under room temperature, continuous (CW) emission operation, or high output operation, etc., has not been realized. The realization of a high-performance laser light source that can take the place of carbon dioxide gas lasers, which have been used since priorly as coherent light sources for the infrared range, solid-state lasers, which use wavelength conversion optical crystals, free-electron lasers, which accompany large-scale facilities, etc., (see for example, the literature, C. Sirtori et al., “Low-loss Al-free waveguides for unipolar semiconductor lasers”, Appl. Phys. Lett. vol. 75 (1999) pp. 3911-3913.) is to be hoped.